Cerebellar damage can be caused by tumor, stroke, hemorrhage, or degenerative disease. Ataxia resulting from cerebellar damage is extremely difficult to treat; most interventions include physical therapy. Our long range goal is to help elucidate the mechanisms by which cerebellar damage alters the production of normal movement and provide information that will enhance rehabilitation treatments for ataxia. The proposed studies will test the general hypothesis that the cerebellum adjusts the relative movements between joints and limbs through trial-and-error practice, making movements automatic and efficient. We believe that deficits in automaticity and efficiency combine to make movements far more mentally and physically taxing, leading to a decline in general activity level and function. Experiments will address: (1) whether people with cerebellar damage show degradation of movement automaticity, (2) whether people with gait ataxia show relative scaling deficits of joints within a leg because of an inability to adjust for interaction torques, and (3) whether cerebellar damage interferes with learning to adjust the scaling between legs during walking. To address these aims, kinematic, kinetic, and electromyographic data will be collected from people with cerebellar damage and control subjects as they perform a variety of movements used in everyday function (e.g. walking, stepping over obstacles and reaching while standing). The proposed experiments are designed to more clearly define the nature of impairments caused by cerebellar damage and provide a basis for interventions that can improve the functional limitations of people with cerebellar damage.